Field of the Invention
The present invention relates to an exposure apparatus and a method of manufacturing an article.
Description of the Related Art
An exposure apparatus based on a stepper scheme (sequential exposure scheme) using an ultraviolet lamp uses a rotation shutter for implementing a function of turning ON/OFF exposure light from the ultraviolet lamp, that is, a function of controlling the incidence of light on a substrate. The rotation shutter is formed from a rotating body including light-shielding portions which shield light. The time during which exposure light enters a substrate is controlled by rotating the rotation shutter, thereby obtaining a target exposure amount.
As a mode of driving and controlling the rotation shutter, for example, an integrated exposure control mode is available. In the integrated exposure control mode, first of all, the rotation shutter is driven (rotated) to make a shift from a state (light-shielded state) in which exposure light is shielded to a state (light-transmitted state) in which exposure light is transmitted. In this light-transmitted state, the rotation shutter is stopped. Before the exposure amount reaches the target exposure amount, the rotation shutter is driven to make a shift from the light-transmitted state to the light-shielded state. In this case, the timing at which the driving of the rotation shutter starts is determined in consideration of exposure light entering a substrate until the shift from the light-transmitted state to the light-shielded state is complete, that is, an exposure amount. In the integrated exposure control mode, it is possible to accurately control an exposure amount. However, the rotation shutter must be driven twice per exposure process. It is therefore a challenge to shorten the time required for exposure processing.
In order to shorten the driving time of the rotation shutter, therefore, Japanese Patent Laid-Open No. 4-229843 has proposed a mode of continuously driving the rotation shutter without stopping it until the light-shielded state is restored after shifting to the light-transmitted state, that is, a so-called continuous driving mode. In the continuous driving mode, the relationship between the rotational speed of the rotation shutter and an exposure amount is obtained in advance, and the rotational speed of the rotation shutter is controlled to obtain a target exposure amount based on the obtained relationship.
As a technique associated with the driving and control of the rotation shutter, Japanese Patent Laid-Open No. 2008-118062 has proposed a technique of executing a low-speed exposure mode for the first substrate of a lot and executing a high-speed exposure mode for the second and subsequent substrates of the lot. In the low-speed exposure mode, while the intensity of exposure light entering a substrate is decreased, a pulse count corresponding to outputs from an optical sensor is counted, and the rotation shutter is closed when the pulse count reaches a target pulse count, and the open time of the rotation shutter is stored. In contrast to this, in the high-speed exposure mode, first of all, a target exposure light for the second and subsequent substrates is corrected from the open time of the rotation shutter, which is stored in the low-speed exposure mode, thereby calculating a final target exposure amount. The rotational speed of the rotation shutter is then decided to become the final target exposure amount based on an approximation function or table indicating the relationship between the rotational speed of the rotation shutter and an exposure amount, which is stored in a memory.
An ultraviolet lamp as a light source for exposure light, however, gradually decreases in illuminance obtained in accordance with the time of use. In the continuous driving mode disclosed in Japanese Patent Laid-Open No. 4-229843, therefore, the optimal rotational speed of the rotation shutter changes relative to a target exposure amount in accordance with the time of use of the ultraviolet lamp. As a consequence, in the continuous driving mode, the accuracy of an exposure amount based on the rotation shutter gradually decreases, and an actual exposure amount deviates from a target exposure amount, thereby failing to obtain a desired exposure result.
In order to avoid such a problem, the relationship between the rotational speed of the rotation shutter and an exposure amount may be obtained again by periodical maintenance to maintain the accuracy of an exposure amount based on the rotation shutter within a predetermined range. To maintain the accuracy of an exposure amount required recently, it is necessary to shorten a maintenance cycle. This leads to decreases in the operating rate of an exposure apparatus and productivity.
In addition, the technique disclosed in Japanese Patent Laid-Open No. 2008-118062 gives no consideration to the time of use of an ultraviolet lamp, that is, a decrease in the illuminance of exposure light. Even if, therefore, the rotational speed of the rotation shutter is decided by using the approximation function or table indicating the relationship between the rotational speed of the rotation shutter and an exposure amount, which is stored in the memory, a final target exposure amount cannot be obtained as the time of use of the ultraviolet lamp increases.